Press for hydrostatic extrusion of tubes

ABSTRACT

A press for hydrostatic extrusion of tubes has a pressure chamber containing a pressure generating fluid and a spacer element arranged in the cylinder with a mandrel axially fixed at its inner end by the spacer tube. The mandrel has a point part cooperating with the die in the cylinder. This point part of the die has a smaller cross-section than the rear part of the die, which rear part is secured to a support from which it is separate. The joint between the support and the inner end of the die is sealed. The pressure exerted by the pressure fluid on the larger part of the mandrel in a direction away from the die is greater than the frictional force between the billet being extruded and the point of the mandrel.

United States Patent [191 Nilsson PRESS FOR HYDROSTATIC EXTRUSION OF TUBES v inventor: Jan Nilsson, Robertsfors, Sweden Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden Filed: Feb.'10, 1972 Appl. No.: 225,073

Assignee:

301 Foreign Application Priority om Mar. 15, i971 Sweden 3277/71 US. Cl. 72/60, 72/264 Int. Cl. B2lc 25/04 Field of Search 72/60, 264

References Cited UNITED STATES PATENTS 8/1968 Fuchs, Jr. 72/60 OTHER PUBLICATIONS Some Considerations of The Mechanics of Hydro- [4 Aug. 14, 1973 static Extrusion by Rozner et al.; page 228; Vol. 277, No. 3; March 1964; J. Franklin institute.

Primary Examiner-Richard J. Herbst Attorney-Jennings Bailey, Jr.

57 ABSTRACT A press for hydrostatic extrusion of tubes has a pressure chamber containing a pressure generating fluid and a spacer element arranged in the cylinder with a mandrel axially fixed at its inner end by the spacer tube. The mandrel has a point part cooperating with the die in the cylinder. This point part of the die has a smaller cross-section than the rear part of the die,

which rear part is secured to a support from which it is separate. The joint between the support and the inner end of the die is sealed/The pressure exerted by the pressure fluid on the larger part of the mandrel in a direction away from the die is greater than the frictional force between the billet being extruded and the point of the mandrel.

11 Claims, 4 Drawing Figures PATENIED AUG 1 4 I975 sum 1 or 3 PRIOR ART PATENIE AUG 1 4 I975 SHEU 2 BF 3 Fig. 2 PRIOR ART Fig 4 54 43 44 4 4 l l I PATENIEU AUG 1 4 i975 SHEET 3 OF 3 PRESS FOR I-IYDROSTATIC EXTRUSION OF TUBES BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a press for hydrostatic extrusion of tubes, having a pressure chamber containing a high pressure cylinder, a pressuregenerating punch insertable in this cylinder and a die arranged in the cylinder. In the pressure chamber is a spacer element, usually a tube, which at its inner end axially positions a mandrel which together with the die forms a gap, in which a tubular billet is shaped to a tube when it is subjected to high all-sided hydrostatic pressure in a liquid surrounding the billet.

2. The Prior Art Nilsson application Ser. No. 753,599, filed Aug. 19, 1968 describes a method of hydrostatically extruding tubes and a means for performing the method. In the pressure chamber is a mandrel which is axially positioned in relation to the die by a spacer tube and is attached in a plate resting on the spacer tube. The attachment of the mandrel in the plate has caused many problems. In many cases the mandrel has broken just at the attachment point.

SUMMARY OF THE INVENTION v The invention relates to a mandrel attachment in a press for hydrostatic extrusion of tubes, which eliminates the problems which have existed so far in getting the mandrel to hold at the attachment point.

According to the invention, a press for hydrostatic extrusion of tubes has a pressure chamber containing a pressure generating fluid and a spacer element arranged in the cylinder with a mandrel axially fixed at its inner end by the spacer tube. The mandrel has a point part cooperating with the die in the cylinder. This point part of the die has a smaller cross-section than the rear part of the die, which rear part is secured to a support from which it is separate. The joint between the support and the inner end of the die is sealed. The pressure exerted by the pressure fluid on the larger part of the mandrel in a direction away from the die is greater than the friction force between the billet being extruded and the point of the mandrel.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further described with reference to the accompanying drawings.

FIGS. 1 and 2 show previous ways of designing the attachment of a mandrel.

FIGS. 3 and 4 show the design and attachment according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings, 1 designates a pressure chamber consisting of a high pressure cylinder 2, a piston 3 insertable in this chamber, and a die 4- inserted at the opposite end of the cylinder. Between the piston 3 and the cylinder 2 and between the die 4 and the cylinder 2 are seals 5 and 6, respectively. A spacer tube 8 resting against the die 4 is arranged in the pressure chamber space 7. In the embodiment shown in FIG. 1, a mandrel 9 is mounted in an annular plate 10 which is supported against the spacer tube 8, so that mandrel is positioned axially in relation to the die. At its rear end the mandrel is provided with a conical attachment part 11 and the ring 10 is provided with a conical annular seat 12 to fit the attachment part. A tubular billet 13 is inserted in the pressure chamber and shaped in the gap 14 between the mandrel and the die to form a tube 15, because of the action of a pressure medium in the pressure chamber space 7. In the spacer tube 8 are openin gs so that the space 7a between the mandrel 9, the plate 10, the spacer tube 8 and the die 4 is in permanent communication with the interior of the pressure chamber space 7. In the embodiment of the die according to FIG. 2, mandrel l7 and plate 18 are made in one piece.

In the passage 20 in the tube 15 the pressure is 1 bar and in the pressure chamber space 7 it is 10-20 kbar. An unbalanced pressure P p-a p(1rd /4) is then exerted on the mandrel 9, where:

P the total axial pressure p the pressure in the pressure chamber a the cross-section of the mandrel at the die opend the diameter of the mandrel at the die opening.

The pressure P is taken up by the plate 10 and transmitted by this plate to thespacer tube 8. It has been found that the mandrel is likely to rupture at or close to the attachment point even if the attachment point is extremely carefully dimensioned and shaped. In the embodiment according to FIG. 1 the mandrel usually ruptures at the conical part 11 a distance a above the edge 21 in the conical seat 12 of the ring 10. The rupture probably occurs because at this section an extremely high combined tension is obtained because of the unbalanced pressure, the contact pressure between the conical part 11 of the mandrel and the seat 12 and bending stresses in the conical part 11 due to the deformation of the ring 10 under the load P. The embodiment according to FIG. 2 presents an even greater risk of rupture just at the transition between the mandrel l7 and the plate 18.

In the construction and attachment of a mandrel according to the invention, for example as shown in FIG. 3, the risk of mandrel rupture can be decreased. A mandrel 25 has a conical attachment part 26 at its inner end. The plate 27 is solid and is provided with a machined guide 28 for the conical attachment part 26 of the mandrel. A sealing ring 31, for example an O-ring or the like, is placed around the attachment part 26 and is pressed by means of an annular holder 29 against the part 26 and the guide 28. A seal is therefore obtained between the mandrel part 26 and the plate 27, so that pressure medium is prevented from penetrating into the space 30 between the mandrel and the plate 27. The unbalanced pressure P a p p (1rd I/4) is taken up directly by the plate 27 and therefore does not affect the mandrel 25. The tension in the mandrel attachment is therefore decreased. The attachment must be able to take up the tensile force F which occurs because of friction between the billet l3 and the front part of the mandrel 25. The pressure can be considerably reduced if the front part of the mandrel is made conical. The pressure medium in the space 7a acts on the conical part 26 of the mandrel. An upwardly directed pressure P is thus obtained which balances the friction force F. The pressure P p (1r/4) (d d where p the pressure in the pressure chamber d, the diameter of the mandrel d the diameter of the attachment.

The diameter d should be chosen so great than F, 2 F. The mandrel may be provided with a drainage channel 31 to drain the space 30 so that any oil which penetrates will not jeopardize the strength of the joint.

In the embodiment according to FIG. 4, the transition between the larger and small cross-sections of the mandrel is close to the front end and is used in the invention to attach a mandrel point of wear-resistant material on a mandrel otherwise consisting of some other material. A plate 40 resting against the support tube 8 has a cylindrical machined guide 41 with a triangular bevel 42. A cylindrical mandrel part 43 is provided with an attachment ring 44. The mandrel part 43 is pressed against the plate 40 by a ring 45 attached to the plate. ln the triangular space between the bevel 42, the mandrel part 43 and the ring 44 is a sealing ring 46, for example an O-ring. The mandrel is provided with a point 47. The joint between the mandrel part 43 and the point 47 is bridged by a sleeve 48 having sealing rings 49 and 50 which seal between the sleeve 48 and the mandrel part 43 and between the sleeve 48 and the point 45, respectively. The pressure medium acts on the conical surface 51 and gives rise to an axial pressure component where p the pressure in the pressure chamber d the largest diameter of the mandrel point and the rest of the mandrel d,= the smallest diameter of the mandrel point.

The pressure component P forces the point 47 against the mandrel part 43 and this part against the plate 40.

The spaces 50 and 51 can be drained through the channels 52 and 53.

I claim:

1. Press for hydrostatic extrusion of tubes, having a pressure chamber containing a high-pressure cylinder, a pressure-generating punch insertable in the cylinder, a die arranged in the cylinder, a spacer element arranged in the cylinder and a mandrel axially fixed at its inner end by the spacer element, the mandrel having a point part cooperating with the die to form a gap in which a tubular billet is shaped to a tube when it is subjected to an all-sided hydrostatic pressure, the part of the mandrel projecting into the die having a smaller cross-section than the rear part, and a support member separate from the mandrel, the inner end of the mandrel abutting the support member, and means sealing such abutting inner end in a liquid-tight manner with respect to said support member.

2. Press according to claim 1, in which the inner end of the mandrel has a larger cross-section than the point part and said support includes a plate resting on the spacer element.

3. Press according to claim 2, in which the mandrel has a conical rear part.

4. Press according to claim 2, in which the side of the plate facing the die is shaped with a guide surface to center the mandrel.

5. Press according to claim 4, in which said sealing means comprises an annular seal arranged to seal between the mandrel and the guide surface.

6. Press according to claim 3, which includes mechanical retaining members securing the mandrel to the plate.

7. Press according to claim 1, in which the mandrel is conical adjacent the front part.

8. Press according to claim 1, in which the point portion has a smaller cross-section than a following part and means are provided sealing the point of the mandrel in a liquid-tight manner to the following part of the mandrel.

9. Press according to claim 8, including a sleeve bridging the joint between the point part and the following part of the mandrel, said sealing means sealing said sleeve to both said parts of the mandrel.

10. Press according to claim 9, in which said sleeve has grooves therein and said sealing means comprises rings in grooves in the sleeve.

11. Press according to claim 1, in which the mandrel is provided with a drainage channel extending longitudinally therethrough. 

1. Press for hydrostatic extrusion of tubes, having a pressure chamber containing a high-pressure cylinder, a pressuregenerating punch insertable in the cylinder, a die arranged in the cylinder, a spacer element arranged in the cylinder and a mandrel axially fixed at its inner end by the spacer element, the mandrel having a point part cooperating with the die to form a gap in which a tubular billet is shaped to a tube when it is subjected to an all-sided hydrostatic pressure, the part of the mandrel projecting into the die having a smaller cross-section than the rear part, and a support member separate from the mandrel, the inner end of the mandrel abutting the support member, and means sealing such abutting inner end in a liquidtight manner with respect to said support member.
 2. Press according to claim 1, in which the inner end of the mandrel has a larger cross-section than the point part and said support includes a plate resting on the spacer element.
 3. Press according to claim 2, in which the mandrel has a conical rear part.
 4. Press according to claim 2, in which the side of the plate facing the die is shaped with a guide surface to center the mandrel.
 5. Press according to claim 4, in which said sealing means comprises an annular seal arranged to seal between the mandrel and the guide surface.
 6. Press according to claim 3, which includes mechanical retaining members securing the mandrel to the plate.
 7. Press according to claim 1, in which the mandrel is conical adjacent the front part.
 8. Press according to claim 1, in which the point portion has a smaller cross-section than a following part and means are provided sealing the point of the mandrel in a liquid-tight manner to the following part of the mandrel.
 9. Press according to claim 8, including a sleeve bridging the joint between the point part and the following part of the mandrel, said sealing means sealing said sleeve to both said parts of the mandrel.
 10. Press according to claim 9, in which said sleeve has grooves therein and said sealing means comprises rings in grooves in the sleeve.
 11. Press according to claim 1, in which the mandrel is provided with a drainage channel extenDing longitudinally therethrough. 